The present invention relates to bearing structures, spindle motors, and hard disk drives. More particularly, the present invention relates to bearing structures, spindle motors, and hard disk drives with measures against electrostatic problems.
One conventional hard disk drive (hereinafter referred to as a xe2x80x9cHDDxe2x80x9d) is schematically indicated in FIG. 10. In the drawing, an HDD 100 is made of two major components; a disk section 110 and a head section 120 both being housed in a housing 130. The disk section 110 is made of a spindle motor 111 which rotates at high speed, and a plurality of storage media 90 having information storage surfaces and being mounted on a periphery of the spindle motor 111. The head section 120 is made of a plurality of head assemblies 121 which access the information storage surface of the storage media 90 rotating at a high-speed so as to record or replay necessary information, a carriage 125 which supports the head assemblies 121, and a head mount 128 which performs a pivot operation of the carriage 125 allowing the head assemblies 121 to access information on each storage media 90.
In response to recent needs for storage devices with smaller size, higher speed, and larger capacity, a hydrodynamic bearing tends to be used for a spindle motor 111 in place of a conventional ball bearing to implement a rotation with high speed of 10,000 rpm. or more with high accuracy. Especially, an attention has been directed to the use of a spindle motor with a hydrodynamic gas bearing which is free from heating during high-speed rotation and easy to be handled.
FIG. 11 shows an example of the spindle motor 111 having a hydrodynamic gas bearing. In this drawing, a column like shaft 113 is fixed to a base 112, and a hollow cylinder-shaped sleeve 114 is fitted to the outer peripheral surface of the shaft 113 leaving a certain clearance therebetween. The outer peripheral surface of the shaft 113 and the inner peripheral surface of the sleeve 114 constitute a radial bearing section. Opposed to one end face of the sleeve 114 in an axial direction, a disk-shaped thrust plate 115 is attached to the base 112 perpendicular to the axis of the shaft 113. On the surface of the thrust plate 115 opposed to one end face of the sleeve 114, there is provided a groove 116 as shown in a dotted line for generating a thrust hydrodynamic pressure. The end surface of the sleeve 114 and the thrust plate 115 constitute a thrust bearing section The radial bearing section and the thrust bearing section constitute the hydrodynamic gas bearing, and a gas (normally the air) present between the components of each bearing section generates a hydrodynamic pressure by relative rotating movements of the components. A rotor hub 117 is fixed to the sleeve 114, and a plurality of storage media 90 are mounted on the outer peripheral surface of the rotor hub 117. Attached also to the base 112 is a radially-disposed stator 118, which is wound with a coil. On the inner peripheral surface of the rotor hub 117, there is mounted a rotor magnet 119, which is faced with the stator 118.
In operation of spindle motor 111 so constructed, an electric current supplied to the coil wound around the stator 118 induces repellent/attraction forces between the stator 118 and the rotor magnet 119. This produces a rotational driving force of the rotor hub 117, which drives the sleeve 114 fixed to the rotor hub 117 to rotate about the shaft 113. This rotation generates hydrodynamic pressure in a radial direction at the radial bearing section, and this keeps the shaft 113 and the sleeve 114 out of contact with each other. On the other hand, in the thrust bearing section, the relative rotation between the end face of the sleeve 114 and the thrust plate 115 generates a hydrodynamic pressure in a thrust direction by the effect of the groove 116. As a result, the sleeve 114 is lifted up from the thrust plate 115, which makes the sleeve 114, the rotor hub 117, the storage media 90, and other rotatable components out of contact with the shaft 113, the thrust plate 115, and other fixed components, thereby enabling a high-speed rotation.
As described above, the use of a hydrodynamic gas bearing provides the spindle motor 111 with stable and high-speed rotation. The high-speed rotation in a non-contact state, however, has problems, For example, the high-speed rotation causes an air friction, which generates an electrostatic charge in the rotatable components. The electrostatic charge is accumulated in the rotatable components since they are isolated from the fixed components. The bearing section with the ball bearing allows the electrostatic charge to flow into the fixed components being in contact with the ball bearing, which causes no problems. On the other hand, since the rotatable components of the hydrodynamic bearing are out of contact with the fixed components, the electrostatic charge generated in the rotatable components is prevented from leaking to the fixed components.
The electrostatic charge, if it is accumulated to a certain extent, can cause an electrostatic discharge between, for example, the disc section 110 and the head section 120 of the HDD (see FIG. 10). This may in turn damage the head assemblies 121, the storage media 90, and other HDD components. The same problem can occur in other bearings such as magnetic and hydrostatic gas bearings in which the rotatable components are rotated without any contact with the fixed components.
In the hydrodynamic gas bearing, no hydrodynamic pressure is generated as long as the spindle motor is de-energized and then the rotatable components are maintained in contact with the fixed components. Therefore, the bearing member made of conductive material such as stainless steel allows the accumulated electrostatic charge to be discharged by the contacts with the components during the halts of the spindle motor. This means that a relatively short on/off driving of the spindle motor can prevent the accumulation of the electrostatic charge in the rotatable components. A relatively long time rotation without any contacts between the rotatable and fixed components accumulates a great amount of electrostatic charge, which may damage the HDD components.
The bearing components may be made of ceramics having an enhanced abrasion resistance to prevent abrasion and seizing thereof. Typically, the ceramic bearing member is insulative. Therefore, the bearing member made of ceramics disables the electrostatic charge from being discharged even by the contact of the bearing members during the halt of the spindle motor.
Japanese Patent Laid-Open Publication (A) No. 55916/1999 discloses a spindle motor having means for overcoming such problem. FIG. 12 schematically illustrates the spindle motor 140. In the drawing, a base 141 supports a shaft 142 onto which a rotor hub 143 is fitted. On an outer peripheral surface of the rotor hub 143, a hard disk, not illustrated, is to be mounted. A radial bearing component 144 is attached to the shaft 142, and a radial bearing component 145 is attached to the rotor hub 143. The radial bearing component 144 and the radial bearing component 145 are faced with each other leaving a specified clearance therebetween in such a manner as to enable relative rotation thereof. Attached to both axial ends of the rotatable radial bearing component 145 are a pair of thrust bearing components 146 and 147 so that the components face with the bottom face and the top face of the fixed radial bearing component 144, respectively, leaving a specified clearance. The shaft 142, which is equipped with a stator 148 wound with a coil, is faced with a rotor magnet 149 attached to the rotor hub 143 for driving the spindle motor.
In operation of the spindle motor 140 so constructed, an electric current supplied to the coil of the stator 148 produces a rotational driving force between the stator 148 and the rotor magnet 149, which in turn rotates the rotor hub 143 equipped with the rotor magnet 149 about the shaft 142. As a result, the rotatable radial bearing component 145 attached to the rotor hub 143 rotates, thereby generating a radial hydrodynamic pressure between the rotatable radial bearing component 145 and the fixed radial bearing component 144 confronted therewith. At the same time, a thrust hydrodynamic pressure is generated between the rotatable thrust bearing component 146 and the bottom face of the fixed radial bearing component 144 confronted therewith, and between the rotatable thrust bearing component 147 and the top face of the fixed radial bearing component 144 confronted therewith. Consequently, the rotor hub 143 and the rotatable components fixed thereto rotate in non-contact state with the shaft 142 and other fixed components.
In order to discharge the electrostatic charge built up in the rotatable components which rotate in a non-contact state, the spindle motor 140 disclosed in the Japanese Patent Laid-Open Publication (A) No. 55916/1999 has the structure shown below. A ring-shaped magnet 151 and a magnetic plate 152, which are in contact with each other, are attached to the rotor hub 143. Between the magnetic plate 152 and the shaft 142, there is provided a slight gap, and the gap is filled with a magnetic fluid 153. The electrostatic charge generated at the rotatable components are discharged into the fixed components through the magnetic fluid 153.
However, the structure disclosed in Japanese Patent Laid-Open Publication (A) No. 55916/1999 has some problems. For generating hydrodynamic pressure in this bearing structure, a gas should extend between the radial bearing components 144 and 145, between the thrust bearing components 144 and 146, and between the thrust bearing components 144 and 147. In the structure as shown in FIG. 12, an opening to feed/discharge the gas is, as shown with an arrow 150 in the drawing, provided only at the upper end or the lower end of the spindle motor. Consequently, as is clear from the drawing, the gas flow for generating the hydrodynamic pressure passes through a sealing layer sealed by the magnetic fluid 153. Depending on the specifications and working conditions of a bearing, as well as the properties of a sealing component to be used, the incoming gas flow may break the magnetic sealing layer, and the high-speed rotation of the rotor hub 143 may splash the magnetic fluid 153. Once the magnetic fluid 153 is splashed, the rotatable components are no longer in contact with the fixed components, as a consequence of which the electrostatic charge may build up in the rotatable components, leading to possible damages on the HDD.
Another problem is increased power consumption. When the peripheral speed of the rotatable components sealed by the magnetic fluid 153 becomes higher to a certain extent, the magnetic fluid 153 filling the gap between the fixed components and the rotatable components develops a large viscous resistance. This increases the rotational driving torque and consequently increases the power consumption. In addition, an increase of the viscous resistance causes generation of heat, which increases the temperature of the whole HDD.
When ceramics, which are generally nonconductive and have high abrasion resistance, are used at the bearing sections, it is impossible to discharge electrostatic charge built up in the rotatable components even if the bearing components are in a contact state at the time the spindle motor stops. As a result, damages on the HDD may occur by the accumulation of electrostatic charge, which may lead to forced replacement of ceramics with conductive materials such as a stainless steel, even though ceramics have good abrasion resistance as bearing components.
The object of the present invention is to solve the problems stated above. More particularly, it is an object of the present invention to provide bearing structures, spindle motors, and HDDs having a structure for reliably discharging electrostatic charge built up at rotatable components during rotation to fixed components even they rotate in non-contact state. It is another object of the present invention to provide a bearing structure which is capable of conducting electrostatic charge when it comes to contact state at the time rotation stops, while keeping excellent abrasion resistance and rigidity.
One aspect of the present invention relates to a bearing structure, comprising: fixed components; and rotatable components which are supported by the fixed components for rotation, wherein the fixed components and the rotatable components are kept out of contact with each other during rotations of the rotatable components, and the bearing structure further comprising a conductive structure for electrically connecting the fixed components and the rotatable components is provided on or in the vicinity of an axis of the rotational center of the bearing structure.
Another aspect of the present invention relates to a bearing structure, wherein the conductive structure comprises magnetic fluid.
Yet another aspect of the present invention relates to a bearing structure, wherein the conductive structure is an elastic component which is fixed to one of either the fixed components or the rotatable components and in contact with the other thereof.
Yet another aspect of the present invention relates to a bearing structure, wherein the elastic component is a curved flexible conductive strip.
Yet another aspect of the present invention relates to a bearing structure, wherein the elastic component is a flexible conductive ring.
Yet another aspect of the present invention relates to a bearing structure, wherein the conductive structure comprises a conductive headed pin, which is fitted into a blind hole provided on the one of either the fixed components or the rotatable components in a movable manner in an axial direction, and pushed by a elastic body so that a spherical head thereof serving as a contact point is kept in contact with the other thereof.
Yet another aspect of the present invention relates to a bearing structure having the conductive structure, wherein the elastic body is a coil spring made of conductive materials.
Yet another aspect of the present invention relates to a bearing structure, wherein the conductive structure comprises a bundle of conductive fibers, one end of which is bundled and fixed to the rotatable components, and the other end of which is a free end which is inserted into a hole provided on the fixed components.
Yet another aspect of the present invention relates to a bearing structure, wherein the conductive structure comprises: a spindle which is fitted into and guided by a sleeve fixed to one of either the fixed components or the rotatable components in a manner capable of relative rotation, which spindle has a groove or grooves on an outer peripheral surface thereof for generating hydrodynamic pressure to generate thrust force for pushing a spherical contact point at one end of the spindle into the sleeve by the effect of the relative rotation; and a strand composed of conductive fibers, one end of which is fixed to the other of either the fixed components or the rotatable components and the other end of which is fixed to an end opposed to the spherical contact point of the spindle with having sagging.
Yet another aspect of the present invention relates to a bearing structure, wherein the conductive fibers are composed of any one of boron, carbon monofilaments, or tungsten, or a combination thereof.
Yet another aspect of the present invention relates to a bearing structure, wherein means for supporting the rotatable components in non-contact slate against the fixed components is a hydrodynamic gas bearing.
Yet another aspect of the present invention relates to a bearing structure, wherein one or more bearing components constituting a radial bearing section and a thrust bearing section of the hydrodynamic gas bearing are made of ceramics.
Yet another aspect of the present invention relates to a bearing structure having a hydrodynamic gas bearing, comprising: fixed components; and rotatable components which are supported by the fixed components for rotation, wherein the fixed components and the rotatable components are kept in non-contact state during rotation of the rotatable components, and wherein among bearing components constituting a radial bearing section and a thrust bearing section of the hydrodynamic gas bearing, at least a pair of bearing components coming into contact with each other when rotation stops is made of conductive ceramics.
Yet another aspect of the present invention relates to a bearing structure, wherein the conductive ceramics are made of Al2O3-30 vol. % TiC, TiB2, or Si3N4-30 vol. % TiN.
Yet another aspect of the present invention relates to a bearing structure having a hydrodynamic gas bearing, comprising: fixed components; and rotatable components which are supported by the fixed components for rotation, wherein the fixed components and the rotatable components are kept in non-contact state during rotation of the rotatable components, characterized in that there is provided a conductive structure comprising a magnetic fluid for electrically connecting the fixed components and the rotatable components either in the region where there is no air flow generated by suction or discharge of a gas for generating hydrodynamic pressure at the hydrodynamic gas bearing potion, or in the region where the air flow is negligible.
Still another aspect of the present invention relates to a spindle motor having the bearing structure according to any one of aspects stated above.
Still another aspect of the present invention relates to a hard disk drive having the spindle motor stated above.
Still another aspect of the present invention relates to a HDD, comprising: a plurality of storage media which enable recording or replaying information, or both thereof; a spindle motor which rotates a plurality of the storage media mounted thereon; and a plurality of head assemblies each of which access each information storage surface of a plurality of the storage media, and perform recording or replaying information, or both thereof in non-contact state with the rotating information media, wherein there is provided a discharge induction structure for inducing discharge of electrostatic charge between a dummy disk specified among a plurality of the storage media and a dummy head specified among a plurality of head assemblies.
Yet another aspect of the present invention relates to a HDD, wherein the discharge induction structure is so structured that a gap between the dummy head and the dummy disk is smaller than a gap between other storage media and other head assemblies accessing thereto during operation in a non-contact state.
Yet another aspect of the present invention relates to a HDD, wherein a gap between the dummy head and the dummy disk is about a half of or less than a half of a gap between other storage media and other head assemblies accessing thereto.
Yet another aspect of the present invention relates to a HDD, wherein a gap between the dummy head and the dummy disk is 15 nm or less.
Yet another aspect of the present invention relates to a HDD, wherein the discharge induction structure is so structured that conductivity of the dummy disk is higher than conductivity of other storage media.
Yet another aspect of the present invention relates to a HDD, wherein the discharge induction structure is so structured that conductivity of at least either one of the dummy head or a carriage supporting the dummy head is higher than conductivity of other head assemblies or other carriages, respectively.
Yet another aspect of the present invention relates to any one of the HDD stated above, wherein the spindle motor for driving the storage media has a hydrodynamic gas bearing.
Yet another aspect of the present invention relates to a HDD, wherein one or more bearing components constituting a radial bearing section and a thrust bearing section of the hydrodynamic gas bearing are made of ceramics.
Still another aspect of the present invention relates to a method for avoiding damages caused by electrostatic charge in a hard disk drive having a plurality of head assemblies each of which accesses each of the plurality of rotating storage media for performing recording or replaying information, or both thereof between the head assemblies and the storage media, comprising the step of inducing an electrostatic charge built up in either one of the head assemblies or the storage media to be discharged to the other thereof between a storage medium specified among a plurality of the storage media and a head assembly specified among a plurality of the head assemblies, so as to eliminate damages attributed to discharge of electrostatic charge from other components composing the hard disk drive.
In the bearing structure having a conductive structure using a magnetic fluid according to the present invention, the gas flow passing through the bearing, and a relative rotation at a place of the magnetic fluid disposed are almost negligible. This prevents the air flow from splashing or scattering the magnetic fluid present between the rotatable components and the fixed components, depresses increase of viscous resistance of the magnetic fluid or generation of heat thereof in a high-speed rotation region, and realizes stable discharge of electrostatic charge built up in the rotatable components to the fixed components.
According to the hydrodynamic gas bearing using conductive ceramics materials, high rigidity and good abrasion resistance that ceramics has can be fully utilized for the bearing components, and on the top of that, the electrostatic charge built up in the rotatable components can be safely discharged to the fixed components when the rotatable components come into contact with the fixed components when rotation stops.
According to the hydrodynamic bearing structure in accordance with the present invention, in which a structure for enabling conduction of electrostatic charge is disposed between the rotatable components and the fixed components of the bearing sections, power consumption is constrained. Further, abrasion of a contact point, displacement of a abrasion spot due to scattering abrasion powders, and generation of unnecessary frictional heat are prevented without rotational torque increase stems form contact between conductive materials In addition, the contact between the conductive materials does not hinder lifting up of the rotor hub by the effect of a hydrodynamic pressure groove of a thrust hydrodynamic bearing, nor induce misalignment of the center attributed to conductive materials when assembling the rotatable components and fixed components.
By implementing the HDD having a dummy disk and a dummy head according to the present invention, discharge of electrostatic charge accumulated at the rotatable components of a spindle motor will be induced in between the dummy disk and the dummy head of the present invention, which prevents occurring discharge at other head assemblies of the HDD, resulting in prevention of damages on these regular head assemblies, thereby securing high reliability of the HDD.